Answer:
During the Age of Discovery, which is when Christopher Columbus arrived in the Americas, and first came into contact with not just the land, but also its inhabitants, the contact between these first Europeans with the indigenous peoples of the continent was almost mystical, which means, neither one made much sense of who the other was, in terms of humanity. This started to change as the purpose of the Europeans became not to discover, but to colonize.
1. In terms of relations, when the Spanish finally started to colonize, and not just discover, the new lands of the Americas, the initial relations between Europeans and natives was a good one. To the Europeans, Indians were a novelty, and to the Indians, Europeans were almost like demi-gods, so they were treated as such; with reverence and awe. But when the Europeans began to settle, and colonize in the full sense of the word, these relations changed to much more hostile, on both sides. The Spanish began to enslave the Indians and to alter their systems: language, traditions, religion, etc. The Indians, on their parts, at least the stronger tribes, and the civilizations, like the Incas, fought back against the Spanish invasion.
2. As said, when Columbus first arrived in the Americas, in the 15th century, Europeans saw Indians as a novelty, something strange, but still not totally comprehensible to them. Later, in the 16th century, and even at the end of the 15th century, this image changed and the Indians became known as barbarians, or savages, that needed to be civilized. Thus, a lot of differences ensued: the Spanish began to educate the savages on their religion, and language, and while the Indians honored and venerated the Earth, the Spanish used the resources for development without much care for the environment. These issues created even further tension, although in some instances, and thanks to the impact of Catholic missions in the Americas, adaptation and understanding began to grow a bit. While at first the Indians had been placed under slavery, between the 15th and 16th century, when the Catholic missions arrived, this changed as the Spanish crown was forced to see that slavery was decimating the Indian populations.
3. Words like "savage", "heathen" and "barbarian" were used to define Indians and give them a status below that of Europeans. Many Europeans saw Indians as less than human, but a little above animals. They were thus treated without the respect that a fellow human being, especially of European origin, were afforded.